VEGETABLE FOOD. 275 



Maiden earth has not been investigated by the 

 chemist so thoroughly as it should be. They have 

 attended more to the analysis of what are supposed 

 to be manures, than to those qualities of natural soils 

 which are so eminently salubrious to vegetation. 

 We are still ignorant whether this quality be a 

 chemical or physical body ; or whether some latent 

 principle set at liberty or brought into action by the 

 plough or spade. Certain it is, however, that the 

 first crops on newly broken up land are always superior 

 to those that follow, and when a garden soil becomes 

 " worn out/' as it is called, it can only be renewed 

 by removing the old, and replacing it with an equal 

 quantity of fresh earth from a common or old 

 pasture. 



As a mixture or change of plants on the same 

 spot arrive at greater perfection than if one sort only 

 were sown by itself, or repeatedly sown or planted 

 on the same place, it has been reasonably supposed, 

 that different plants require different kinds of food*. 

 On this supposition the system of what is called 

 " convertible husbandry" and the different courses 

 of cropping adopted by agriculturists are founded ; 

 and the uniform success attending such procedure is 

 sufficient proof of its propriety. Hence the value, 

 and necessity of composts being formed of every kind 



* It is believed by some botanists that every plant has the power 

 of disgorging matters which are hurtful to the system, by which the 

 soil becomes unfit for others of the same kind. 

 T 2 



